Superconducting Characteristics of the Penson-Kolb Model

Abstract

We study superconducting properties of the Penson-Kolb model, i.e. the tight-binding model with the pair-hopping ( intersite charge exchange) interaction J. The evolution of the critical fields, the coherence length, the Ginzburg ratio, and the London penetration depth with particle concentration n and pairing strength are determined. The results are compared with those found earlier for the attractive Hubbard model.PACS numbers: 74.20.-z, 71.28.-1d, 74.25.Ηa General formulationThe Penson-Kolb (PK) model is one of the conceptually simplest phenomenological models for studying superconductivity in systems with short-range, almost unretarded pairing [1,2]. It includes a nonlocal pairing mechanism (the pair hopping term J) that is distinct from the on-site interaction in the attractive Hubbard (ΑΗ) model and that is the driving force of pair formation and also of their condensation. Thus, the superconducting properties can be essentially different in these two models [2]. In the paper we focus on the PK model with arbitrary particle concentration and discuss its superfluid characteristics which have not been considered up to now. In the analysis we have used a linear response theory [3,4] and the electromagnetic kernel has been evaluated within HFA-RPA scheme. The model Hamiltonian has the following form:where t is the single electron hopping integral, J is the pair hopping (intersite charge exchange) interaction, the limit (ii) restricts the sum to nearest neighbors (nn). The Peierls factors in (1) account for the coupling of electrons to the magnetic fleld via its vector potential A(r): Φij = (-e/ħc) fRjRi dvA(r), and e is the electron charge.(217)

Phase Diagrams of the Penson-Kolb-Hubbard Model with Repulsive Pair-Hopping Interaction

“…The electronic spectrum of the η-phase consists of two branches E [9,16,17], which is in contrast with the s-wave phase, where E g > 0 for any T < T c .…”

“…For more detailed discussion of these two η states see Ref. [9,[16][17][18]. In addition to the ground state phase boundaries, we denote in the figures the crossovers to the BEC regimes (dasheddotted lines).…”

“…also [2,[16][17][18]). This behaviour is in contrast with the properties of the isotropic s-wave state, which for U ≤ 0 is stable for any attractive J > 0, and the system exhibits a smooth crossover from the BCS-like limit to the BEC regime with increasing J [2,6,[19][20][21][22]. In the case of η pairing we have also found the crossover to BEC regime which can take place in the range of stability of strong-η phase as electron density is reduced (cf.…”

“…The analysis of electromagnetic properties of the model and consideration of mixed orderings and phase separated states will be presented elsewhere [16].…”

Electron Orderings of Half-Filled Extended Hubbard Models with Spin- and Charge-Exchange Interaction

“…The extended Hubbard models (EHM) (i) with anisotropic spin-exchange interaction (the t−U −J −J ⊥ model [1][2][3][4][5]) and (ii) with charge-exchange (pair hopping) interaction (the t−U −I model, which is also called the Penson-KolbHubbard model [6][7][8][9][10]) are interesting (conceptually simple) phenomenological models for studying correlations and for description of superconductivity, magnetism, and various other types of electron orderings in narrow band systems.…”